Colombo Gabriele, Kim Sunhyung, Schweizer Thomas, Schroyen Bram, Clasen Christian, Mewis Jan, Vermant Jan (2017), Superposition rheology and anisotropy in rheological properties of sheared colloidal gels, in Journal of Rheology
, 61(5), 1035-1048.
Schroyen Bram, Swan James W., Van Puyvelde Peter, Vermant Jan (2017), Quantifying the dispersion quality of partially aggregated colloidal dispersions by high frequency rheology, in Soft Matter
, 13(43), 7897-7906.
Dockx Greet, Verwijlen TOm, Samples Wouter, Nagel Mathias, Moldenaers Paula, Hofkens Johan, Vermant Jan (2016), Simple microfluidic stagnation point flow geometries, in Biomicrofluidics
, 10(4), 043506.
Jacob Alan R, Poulos Andreas S, Kim Sunhyung, Vermant Jan, Petekidis George (2015), Convective Cage Release in Model Colloidal Glasses., in Physical review letters
, 115(21), 218301-218301.
The goal of this project is to make a significant step in the understanding of the flow behaviour of colloidal gels. These soft materials exhibit a number of technologically important properties, such as a yielding (solid-liquid transition) and a complex time dependent behavior of the viscosity called thixotropy. Whereas these features have been extensively documented in literature, the prediction of the elastic properties from the fundamental properties of the suspension (concentration, shape, interaction potential, flow history) remains challenging, and different theoretical approaches diverge and do not predict gel properties adequately. Similarly, thixotropy has so far escaped a micromechanical description. Recently, it has been suggested that the elastic modulus of a suspension can be simply related to the volume fraction and the rigidity of elastic clusters, even when they do not percolate. It has been suggested that the volume fraction of load bearing structures provides a conceptual framework to quantitatively connect the flow-induced microstructure of soft materials to their nonlinear rheology, possibly even their thixotropic response. So far, an array of scattering techniques has been used on a wide range of colloidal gels composed of spherical particles, and whereas the microstructure has been shown to change over many length scales and being spatially very anisotropic, no direct link between the observations and the different concepts has been presented. One of the main reasons seem to be that yielding phenomena and the changes in microstructure are highly localized, as shown in recent experiments in our group in 2D. These may not be adequately detected or described in scattering experiments, which average over the entire volume. In the present work, we will use both novel techniques and suitable model systems that can be directly used to assess critically recent ideas and concepts. On the experimental side we will turn to advanced ultra high speed confocal techniques (> 1000 images per second) developed in our group, which should enable us to identify the mechanisms and phenomena time and spatially resolved in 3D, especially around the yielding transition. Second we will use model systems with non-spherical building blocks. Changing the particle shape (towards both prolate and oblate) while maintaining the same strength of interaction potential, allows us to evaluate the local strength of the elastic clusters by control of the coordination number, which depends on the aspect ratio of the particles. Using even finer control, we can make the particles directionally interacting, which should offer superb control over the local cluster structure. We will tailor the gel microstructure by using particle shape, flow and sample preparation history and varying the type of interaction (depletion, electrostatic, sticky interaction). A particular question, which we intend to answer, is how local particle connectivity controls the mechanical response.